Resturant calories

I eyeball it and estimate the weight

Restaurant website, or check for similar meal at similar restaurants website. If that fails, I just ballpark it as a total amount, and I have private food entries for 100 cals each so I just guess it's X amount of those.

I'll usually plan ahead what I intend to have at a restaurant, and if needed maybe consume a bit less earlier in the day.

If we accept that to lose weight we need to be in the ballpark more often than not but not necessarily always, then we eat like a reasonable person, make a best guess and keep on going.

It does boil down to: you can't know for sure if you're not the one making it. It will always be a guess, sometimes more and sometimes less correct.

But does it matter that much if it is a once in a while thing?

If it does matter, then it is not strictly a logging problem, it becomes more of restaurant eating strategies issue, some of which also help with the logging issues.

In any case: a quick picture of your plate is a good start for post meal logging

Best guess using comparable recipes in the database. It's wrong in the absolute precise sense, OK in the general sense. I don't strees too much on this as I minimize my eating out. Vacations, however, is an issue. I try to be generally "sort of good" while away from home, and use my scale weight before and after to determine if I was. It's a vacation after all, lol.